There are 24 members on a swim team. how many different combinations of 5 swimmers can be chosen to sit in the front row for a team photo?

The number of combinations for picking a number of items from a given selection is found using this formula: nCr = n!/(n - r)!r! where:
n = size of the selection
r = number of items being picked
In the case of the question, there is a selection of 24 people of which 5 will be chosen to sit in the front row so:
n = 24
r = 5
The number of combinations is 24C5 = 42504
Note: scientific calculators, e.g. Casio ones, have a button for the nCr formula.